Oil sands (which are deposits of sand impregnated with bitumen, or viscous oil) are a well-known source of oil. For example, it has been estimated that approximately 175 billion barrels of bitumen can be recovered, using current technology, from the oil sands located in the province of Alberta, Canada. While some of the oil from the oil sands in Alberta can be and is produced by open-pit mining, unfortunately open-pit mining can reach only a small fraction of the available oil sand deposits. The bulk (approximately 81%) of the oil sand reserves established in Alberta is too deep below the surface to be mined and must be extracted using in situ techniques.
Several well-known methods are used for in situ recovery of bitumen from oil sands. These methods all involve substantial cost. For example, a primary method for in situ oil sands recovery of bitumen is “Steam Assisted Gravity Drainage” or SAGD. This method involves drilling two horizontal wells, the top well being used to inject high pressure steam into the oil sand deposit, and the bottom well being used to collect bitumen which has been heated by the steam to become less viscous and can therefore flow into the bottom well.
It is evident that before bitumen can be extracted from oil sand deposits which are buried below the ground surface, the required oil sand deposits must first be located. To economically justify the installation of bitumen extraction equipment, the oil sand deposit from which bitumen is being extracted must be sufficiently large. Typically the minimum size of an oil sand deposit which would justify installation and use of extraction equipment is 500 m long×500 m wide×30 m deep. These dimensions are approximate and can change with technology and according to a variety of factors (a larger volume could be required to justify stand alone production facilities).
In addition to the above minimum size requirement, there is also a requirement that the oil sand deposit be “clean”. The reference to “clean” means that there should not be any significant quantity of shale present in the deposit. This is because if shale is present in the oil sand deposit, the shale will act as a barrier to both the flow of steam, and the flow of oil, and will severely restrict the volume of oil that can be recovered.
Locating clean oil sand deposits of at least the minimum size needed has in the past required drilling a systematic grid of core holes or exploration wells, and conducting two-dimensional seismic exploration, which can require clear cutting of vegetation. Drilling the exploration wells and conducting seismic, is extremely expensive and can disfigure the landscape. In addition, in some locations, such as northern Alberta, exploration wells can be drilled only at limited times of the year limiting the speed of exploration and development. However, to date there has been no means of determining volumes of clean sand aside from drilling.